Introduction: Combined medullar sclerosis, together with peripheral sensory neuropathies, is the most common neurological manifestation observed in cobalamin deficiency. Biermer's disease [low stomach acid] is the predominant cause. Other clinical and etiological aspects are nevertheless frequent, although underestimated.

Methods: This retrospective study included patients with neurological symptoms and cobalamin (B12 vitamin) deficiency confirmed by laboratory tests collected over a period of 11 years.

Results: Twenty-seven cases were analyzed. Mean age was 47 years and there were 11 women and 16 men. Distribution of the neurological syndromes was: combined medullar sclerosis in 18 patients (67%), sensory neuropathies in 30% of cases and sensory-motor neuropathies in 15%. One patient had fronto-subcortical dementia with good improvement after vitamin replacement.

In addition, autonomic dysfunction was noted in six patients (orthostatic symptomatic hypotension and/or urinary dysfunction and/or erectile failure). Dysautonomia revealed cobalamin deficiency in three patients with a good and fast response to the cobalamin therapy in all cases. Biermer's disease was diagnosed in 17 patients (63%) and a likely syndrome of nondissociation of cobalamin in two patients. One patient had Crohn's disease and no etiology was found in seven patients. In five patients (19%), nitrous oxide undoubtedly induced decompensation of latent cobalamin deficiency; four after a general anesthesia and one by chronic professional exposure.

Outcome was very good in 46% of patients after vitamin replacement, particularly if treatment was started rapidly.

Discussion: The findings in this series highlight the frequency of autonomic dysfunction sometimes revealing cobalamin deficiency with a fast and good response to vitamin replacement and the frequency of neurological disorders following decompensation triggered by general anesthesia using nitrous oxide in patients with latent cobalamin deficiency.